It seems that the Menaphos security will neither allow them to leave nor enter the city farther, causing them to become stranded on the docks until the stalemate has concluded.

The Riddler crab can only be found on certain worlds at certain times as the location is shared with other NPC's that participate in the Jewels of the Elid activity. In order to receive the Alaeite, you will need to correctly answer the riddle posed to you. The answer to the riddle is "crab".